Method of making sheet steel and lubricant-protective composition useful therein



United States Patent 3 252 907 METHOD OF MAKISIG SHEET STEEL AND LU- BRlCANT-PROTECTIVE COMPOSITION USE- FUL THEREIN Issa J. Kharouf, Penn Hills Township, Allegheny County,

and William L. Mathay, Upper St. Clair Township,

Allegheny County, Pa., assignors to United States Steel Corporation, a corporation of New Jersey No Drawing. Filed Mar. 23, 1962, Ser. No. 182,129

3 Claims. (Cl. 252-25) This invention relates to a method for the manufacture of sheet steel, e.g., black plate or tin plate, and a composition used therein, the object being to simplify the process ordinarily followed and make it more economical.

This is a continuation-in-part of our application Serial No. 71,180, filed November 23, 1960, now abandoned.

The modern process of tin-plate manufacture includes cold-rolling low-carbon steel strip substantially to the final gage with lubricating oil on its surface, cleaning to remove rolling oil, annealing in coils or in single ply, temper rolling, cleaning, pickling, electrotinning, heating to melt the tin coating, quenching, then chemically or electrochemically treating the strip in a dilute solution containing chromate ions to increase resistance to discoloration, rinsing in water and finally oiling with cottonseed oil, palm oil, dioctyl sebacate or other lubricant. This process requires repeated handling with uncoiling and recoiling, even though certain combinations of steps are continuous. In a recent further refinement, furthermore, additional cold-rolling is effected after tin plating or after melting the tin coating, to reduce the gage further by a substantial amount. If a rolling oil is used on the strip during this reduction, a second cleaning step must therefore be introduced to remove such oil before the strip is electrochemically treated in a solution containing chromate ions, rinsed and finally oiled, according to the conventional method.

We have invented a novel composition which serves not only as a rolling lubricant for the final rolling of black plate or tin plate but also to form a chemical coating for improved discoloration resistance and a permanent lubricant which remains on the finished product, together with the improved method thereby made possible which eliminates the second cleaning and rinsing of tin plate and takes the place of the separate chemical treatment and final oiling heretofore practiced. Our composition is a water emulsion of palm oil or the like, having chromate ions therein at a concentration sufiicient to form the desired chemical coating. Some of the oil breaks from the emulsion on contact with the strip and not only lubricates the strip during rolling but remains on the strip thereafter as a protective coating.

The invention as applied to the rolling of black plate, i.e., low-carbon sheet steel which is not tinned, gives it improved corrosion resistance by the chromate film formed thereon and the protective coating of oil.

A complete understanding of the invention may be obtained from the following detailed explanation of the method and the typical example of the composition.

In carrying out the invention, we first prepare a concentrated emulsion of palm oil or the like in water by the aid of a suitable emulsifier or wetting agent. For this purpose, we use an alkyl aryl ether of polyalkylene glycol, specifically the reaction product of t-octyl, n-nonyl or dodecyl phenol with ethylene oxide, the structure of which is:

Q where R is a saturated alkyl hydrocarbon radical containing 8 or more carbon atoms and x is an integer greater 3,252,907 Patented May 24, 1966 than 8. More particularly, R is a saturated alkyl hydrocarbon radical selected from the group t-octyl, n-nonyl and dodecyl. Emulsifiers or wetting agents of the type designated are obtainable commercially, i.e., Union Carbide Corporations Tergitol NPX or Rohm & Haas Companys Triton Xl00.

The concentrated emulsion has a composition accord ing to the following formula (percentages by weight):

Percent Oil (palm oil, cottonseed oil, di-n-butyl sebacate, n-butyl stearate, 2-ethylhexyl phthalate or-di octyl sebacate) 40-59 Emulsifier 1 -7 Water 4059 A typical example is: palm oil, 48%, emulsifier, 4%; and water, 48%. Homogenization of the oil and emulsifier with the water gives an immediate emulsion of the oil in the water.

The concentrated emulsion is next diluted with water. We mix from 2 to 25 parts of the concentrated emulsion with from 98 to parts of water. A typical example is 4 parts concentrated emulsion and 96 parts water. It is important to form the concentrated emulsion and then dilute it in order to make the emulsion uniform and to prevent separation of the oil from the water. I

We then add to the dilute emulsion from 7 to 30 grams per liter of chromic acid (C10 for example about 10 grams per liter, or an equivalent amount of a chromate such as Na CrO or K CrO or corresponding dichromates, to give a concentration of chromate ion containing from about 0.3% to 1.6% chromium. The emulsion is stirred and heated to a temperature of from to 180 F., preferably about F., to insure solution of the acid or salt, and is then ready for use as rolling medium in the reduction of tinned strip to final gage or in the final states of the reduction of black plate to the desired gage. While emulsions containing more than 30 g./l. of chromic acid may be used, no significant advantage is obtained thereby.

v1n using the emulsion, it is applied to the tin plate or black plate in any suitable manner. For example, it may be sprayed against both surfaces of the tin-plated strip through nozzles spaced sufficiently close together to provide complete coverage. Preferably the emulsion is sprayed through the nozzles at a rate sufiicient to provide a suitable amount of oil on the strip after it is rolled, e.g., about 0.10 to 0.25 gram per base box. The actual fiow rates through the nozzles necessary to achieve the desired oil-coating weights depend upon a number of factors, as will be explained later. The emulsion partially breaks on contact with the metals, some of the oil adhering thereto and separating from the solution. The tin plate, immediately after the medium has been applied to it, is cold reduced, for example about 50% in a continuous cold-reduction mill, at a line speed of about 800 f.p.m. This produces a light-basis-weight tin plate having the oil coating and chromate film characteristic of such tin plate which has been electrochemically treated and oiled according to the practices known before our invention.

As a specific example of the practice of our invention, a coil of tin-plated strip 36 inches wide, having a basis weight of 112 pounds per base box (lb./bb.), and a tincoating weight of nominally 0.50 lb./bb., was simultaneously cold-reduced, chemically treated and oiled, by cold rolling with emulsion made as explained above, to a final basis weight of 55 lb./bb. (i.e., the thickness of the tin plate was cold-reduced by 50%) by passing it through a rolling mill at a line speed of 840 f.p.m. Before the tin plate entered the mill, it was sprayed on both sides with an emulsion prepared as described above. The total flow Range. Example percent Palm oil or equivalent. 0.8 to 15 3. 5 Emulsificr 0. 02 to 1. 78 0. 5 Chrotnatc ion 7 to 2 1. 5 Water 80 to 98. 5 Q4. 5

The light-basis-weight tin plate produced according to the above specific example appeared to be fully the equivalent of tin plate chemically treated and oiled according to conventional procedures. In particular, the product displayed an oil-coating weight of 0.20 to 1.30 g./bb., a surface chromium content of 0.16 to 0.50 mg./sq. ft. of surface (i.e., both sides) and adequate lacquerability as evidenced by lacquer-wetting tests of the spray, drop and flow types and other tests wherein it was determined that if the product is coated with a phenolic lacquer, satisfactory adherence and resistance to flaking are obtained.

The amount of oil and surface chromium remaining upon the strip after treatment by our method depends upon such factors as the rolling speed, the temperature of the emulsion at the time it is applied, the amount thereof sprayed upon the strip, and the concentrations of oil and chromate ion therein. Higher rolling speeds and higher emulsion temperatures give lighter oil coatings, whereas lower rolling speeds and lower emulsion temperatures have the opposite effect. Since it is desirable to have the oil coating as light as is consistent with a resulting product of adequate lubricity, it is important that the emulsion be able to stand moderate heating without separating. The emulsion prepared according to our invention is thermally stable up to 180 F.

The exact emulsion temperatures, rolling speeds and spray rates to be used in practicing our invention are interdependent. On a test, with rolling speeds in the range of 50 to 100 f.p.m., satisfactory results were obtained with emulsion temperatures of about 130 to 180 F. and spray rates of about 0.8 to 1.0 gal./bb. On a commercial cold-reduction mill, with rolling speeds in the range 350 to 950 f.p.m., satisfactory results were obtained with emulsion temperatures of 130 to 150 F. and spray rates of about 1.0 to 1.25 gal./bb.

The invention may also be applied with advantage in the conventional method of making tin plate since, by the use thereof, the oiling and chemical treatment of the material may be effected in a single step instead of requiring two separate steps as previously necessary. For this purpose, the tin-plated steel strip may simply be passed through the dilute emulsion of lubricant having chromic acid added thereto, although spraying or other methods of application may be employed,

While we have shown and described a preferred practice of our invention, we intend to cover as well any change or modification'therein which may be made without departing from the spirit and scope of the invention.

We c'laimi 1. In the manufacture of sheet steel by cold-rolling sheet steel of intermediate gage to final gage, the improvement comprising flooding the surfaces of the steel during said cold-rolling with an emulsion in water of from 0.8 to 15% by weight of a lubricant selected from the group consisting of palm oil, cottonseed oil, di-n-butyl sebacate, n-butyl stearate, 2-ethylhexylphthalate and dioctyl sebacate, said emulsion also containing chromate ions aifording from about 0.3 to 1.6% by weight of chromium and from 0.02 to 1.78% by weight of an alkyl aryl ether of polyalkylene glycol as an emulsifier for said emulsion, said ether being a compound having the structure v where R is a saturated alkyl hydrocarbon radical containing at least 8 carbon atoms and x is an integer greater than 8, thereby effecting oiling and chemical treatment simultaneously. I

2. The method as defined by claiml, characterized by said emulsifier being the reaction product of ethylene oxide and a phenol selected from the group consisting of t-octyl, n-nonyl and dodecyl phenols.

3. A lubricant and chemical-treatment composition for use in cold-rolling sheet metal comprising an emulsion in water of (a) from 0.8 to 15% by weight of a lubricant selected from the group consisting of palm oil, cottonseed oil, di-n-butyl sebacate, n-butyl stearate, 2-ethylhexylphthalate and dioctyl sebacate, (b) from 0.02 to 1.78% by weight of an alkyl aryl ether of polyalkylene glycol as an emulsifier for the emulsion and (c) chromate ions affording from 0.3 to 1.6% by weight of chromium, said ether being a compound having the structure:

where R is a saturated alkyl hydrocarbon radical containing at least 8 carbon atoms and x is an integer greater than 8.

References Cited by the Examiner UNITED STATES PATENTS DANIEL E. WYMAN, Primary Examiner. R. E. HUTZ, C. F. DEES, Assistant Examiners, 

1. IN THE MANUFACTURE OF SHEET STEEL BY COLD-ROLLING SHEET STEEL OF INTERMEDIATE GAGE TO FINAL GAGE, THE IMPROVEMENT COMPRISING FLOODING THE SURFACES OF THE STEEL DURING SAID COLD-ROLLING WITH AN EMULSION IN WATER OF FROM 0.8 TO 15% BY WEIGHT OF A LUBRICANT SELECTED FROM THE GROUP CONSISTING OF PALM OIL, COTTONSEED OIL, DI-N-BUTYL SEBACATE, N-BUTYL STEARATE, 2-ETHYLHEXYLPHTHALATE AND DIOCTYL SEBACATE, SAID EMULSION ALSO CONTAINING CHROMATE IONS AFFORDING FROM ABOUT 0.3 TO 1.6% BY WEIGHT OF CHROMIUM AND FROM 0.02 TO 1.78% BY WEIGHT OF AN ALKYL ARYL ETHER OF POLYALKYLENE GLYCOL AS AN EMULSIFIER FOR SAID EMULSION, SAID ETHER BEING A COMPOUND HAVING THE STRUCTURE: 